Fibrotic scarring destroys the delicate architecture of the lung, making normal gas exchange impossible. The types of insults that cause such chronic dysfunction are legion, representing nearly every category of disease. Most, however, share an early common feature: exudation of fibrinogen into the procoagulant-rich distal air spaces. A multitude of events follow, leading eventually either to restoration of normal tissue or to deposition of dense, dysfunctional matrix. The role of the fibroblast in the fibrotic process is central. Although fibrinogen, fibrin, and the fragments which result from their enzymatic cleavage are known to stimulate fibroblast chemotaxis and growth, the specific effects of fibrinogen and its derivatives on different types of lung fibroblasts are poorly understood. The primary goal of the proposed research is to describe the mechanisms by which fibrinogen-derived molecules stimulate proliferation and activation of lung fibroblasts. We hypothesize that lung fibroblasts have specific receptors for portions of the fibrinogen molecule which mediate signals for proliferation alteration of the surrounding matrix and modulation of the local inflammatory response. In testing this hypothesis, we will address three primary questions: * Does fibrin(ogen) stimulate lung fibroblast proliferation directly or indirectly? Rat lung fibroblasts will be cultured in the presence of fibrinogen, fibrin and fibrinolytic peptides or in conditioned media from fibrin(ogen)-stimulated cells. Proliferation assays will determine active moieties. Autocrine loops will be defined by measuring mRNA levels for basic FGF, PDGF and IGF-1, and confirmed by measuring their secretion or by using monoclonal antibodies to block their effects. * How do fibrin(ogen)-stimulated fibroblasts alter the matrix and signal the cells which surround them? Expression and secretion of collagen, metalloproteinase inhibitors, and plasminogen activator inhibitors will be measured to define matrix alteration. Elaboration of the inflammatory cytokines IL-I, IL-6 and IL-8 will be explored. * Do subsets of fibroblasts differ in their response to fibrin(ogen)? Surface display of Thy l antigen distinguishes two different and stable phenotypes of rat lung fibroblasts. We will demonstrate differences in their fibrin(ogen)-induced proliferation and activation by stimulating Thy 1(-) and (+) subpopulations separated by FACS. e results of the proposed research will broaden current understanding of the response of fibroblasts fibrin deposition in the lung.